It is known to provide a vehicle transmission that allows the vehicle to execute zero radius turns and spin turns. Military tank vehicles and other tracked vehicles have been provided with a dual differential type of transmission capable of zero radius turns and spin turns. This type of drive and steer transmission is described in the articles entitled Tanks And Dozers Turn On A Dime With New All-Gear Steering, and Tank-Steering Mechanisms. The transmission includes a driving portion having a driving differential which receives rotational power from the vehicle power source for propelling the vehicle during operation. The driving portion includes a drive input control which can be operatively engaged by the operator for varying the speed and forward/reverse direction of the vehicle. The transmission also includes a steering portion having a steering differential. The steering portion includes a steering input control that can be operatively engaged by the operator for executing turns. The steering portion engages the driving portion such that as the steering input control is engaged by the operator to execute a turn the steering portion increases the speed of the track on one side of the vehicle and proportionately decreases the speed of the track on the other side of the vehicle. In this manner the vehicle executes a turn. When the vehicle is stationary, the operator can engage the steering input control, which will cause the tracks on one side of the vehicle to be driven forwardly, and the tracks on the other side of the vehicle to be driven rearwardly at the corresponding speed. This causes the vehicle to execute a spin turn.
As described in the article entitled Tank-Steering Mechanisms, a different transmission having planetary gear arrangements functions in a manner similar to the dual differential drive and steer transmission described above. This type of transmission also includes a driving portion having a driving input control, and a steering portion having a steering input control. The steering portion interacts with the driving portion to increase the speed of the tracks on one side of the vehicle and correspondingly decrease the speed of the tracks on the other side of the vehicle.
These types of drive and steer transmissions allow the vehicle to be highly maneuverable, and allow the vehicle to execute zero radius turns and spin turns. These drive and steer transmissions are typically provided on heavy duty vehicles such as military tanks, bulldozers, and other large tracked vehicles.
If these types of transmissions were controlled by a conventional steering wheel, the vehicle would execute turns in the direction that the steering wheel is turned when traveling in the forward direction of vehicle travel. However, when travelling in the reverse direction, some of these drive and steer transmissions would cause the vehicle to execute a turn to the seated operator's left if a steering wheel were to be turned to the right when driving in the reverse direction of travel, and would execute a turn to the seated operator's right if a steering wheel were to be turned to the left when driving in the reverse direction of travel. These steering characteristics are generally unfamiliar to the general public, who are generally more comfortable and familiar with the steering characteristics of automobiles. Automobiles execute turns to the left when the operator turns the steering wheel to the left when driving in reverse, and execute turns to the right when the operator turns the steering wheel to the right when driving in reverse.
It would therefore be desirable to provide drive and steer transmissions with a mechanism that alters the steering characteristics in reverse so that the transmission steers the vehicle in a manner similar to an automobile. If steering in reverse were to be similar to the steering of an automobile, then more of the general public would be comfortable and familiar with the handling of such a vehicle. This would help allow a drive and steer transmissions to be utilized on vehicles other than large tracked vehicle, such as relatively small residential lawn tractors. Such a vehicle would be highly maneuverable and would steer in directions the direction that the operator turns a steering wheel in a fashion that is familiar to most operators. No special driving skill would be required of the operator.